For the second year, NRDC has a searchable by zip code map that enables beach-bound vacationers to check recent water-quality information.

"Pollution levels have remained constant and we're still seeing the same unacceptable level of closings and advisories every year," NRDC senior attorney Jon Devine told USA TODAY.

The primary cause of beach water pollution is storm runoff from roadways, parking lots and other hardscapes, Devine noted, adding the NRDC wants the EPA to enact stricter rules on how cities manage that runoff.

Swimming in contaminated water can cause a host of maladies from gastrointestinal ailments to pinkeye, though linking an illness to a day at the beach is "extremely under reported," Devine said. "People don't know that water can contain viruses, bacteria and other parasites that make you sick. And when they get sick they don't associate the two."

Overall, the Great Lakes region had the highest violation rates, with 10% of the water samples not meeting clean-water standards. The best scores were from the Delmarva area with 3% of samples in violation.

States with the highest violation rates: Ohio (21%); Wisconsin (14%) and Minnesota (12%). States with the fewest violations: Delaware (less than 1%); New Hampshire (1%); and North Carolina (2%).

NRDC awards up to five stars to 200 popular vacation beaches based on low violation rates, frequent water testing and prompt public notification when there is a problem.